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Firefighters are expecting cloud coverage to increase while they attempt to control the Williams Fire in the Angeles National Forest, which has been scorching thousands of acres for days. More clouds, officials say, means cooler temperatures. Stephanie Elam reports from Irwindale for the NBC4 News at 5 p.m. on Sept. 4, 2012. (Published Tuesday, Sept. 4, 2012)

Updated at 8:32 PM PDT on Tuesday, Sep 4, 2012

Firefighters launched another attack early Tuesday on a 3,600-acre wildfire that started Sunday in Angeles National Forest in Southern California and prompted the evacuation of a popular camping area during Labor Day weekend.

The Williams fire, which started in the Camp Williams park along East Fork Road off Highway 39, might not be contained until next week, according to fire officials. Firefighters are facing steep terrain with dry brush that has not burned for 15 to 20 years.

Crews Launch Aerial Attack on Williams Fire

Fire officials said to expect an "air show" Tuesday when firefighters launch an aerial attack on the Williams fire, which started during Labor Day weekend in Angeles National Forest. Toni Guinyard reports for Today in LA on Tuesday, Sept. 4, 2012. (Published Tuesday, Sept. 4, 2012)

"You're going to see an air show out there today," said Nathan Judy, Angeles National Forest Fire Information Officer.

About 500 firefighters and 21 firefighting aircraft were assigned to the fire. Crews are protecting structures in the Camp Williams area, a camping area from which about 12,000 recreational campers were evacuated from the area during the weekend. Many left camping items and vehicles at the site, and authorities plan to establish a phone number for campers to call so they can collect their property.

Stubborn Williams Fire Could Burn for Days

The Williams Fire, north of Azusa, could burn until next Thursday. Robert Kovacik reports for the NBC4 News at 11pm on Monday, September 3, 2012 (Published Tuesday, Sept. 4, 2012)

Crews will assess Tuesday whether the 75 residents of the East Fork area who were evacuated can return home.

Wind gusts reached 25 mph Monday night after a day of temperatures in the mid-90s and low humidity levels. The fire made several runs, starting at about 3 p.m., along 30- to 80-percent slopes.

Brush Burns Near Azusa

The acreage figure was revised Monday from 4,000 to 3,600 acres after crews obtained updated mapping. Containment was at 15 percent early Tuesday.

"Today, we're looking at high temperatures, low humidity," said Judy. "So, if it makes a push toward the north, going toward the wilderness area, that's what we're going to be keeping our eyes on and hitting that hard with aircraft and getting some boots on the ground to try to complete that line."